Alkali-free glass

ABSTRACT

A subject for the invention is to provide an alkali-free glass which is capable of reducing or totally eliminating As 2 O 3  and which has fewer bubble inclusion than that in the prior technology. 
     The invention relates to an alkali-free glass which comprises SiO 2  in an amount of from 40 to 70% by weight; Al 2 O 3  in an amount of from 6 to 25% by weight; B 2 O 3  in an amount of from 5 to 20% by weight; MgO in an amount of from 0 to 10% by weight; CaO in an amount of from 0 to 15% by weight; BaO in an amount of from 0 to 30% by weight; SrO in an amount of from 0 to 10% by weight; ZnO in an amount of from 0 to 10% by weight, each based on the total amount of said glass, and helium and/or neon in an amount of from 0.0001 to 2 μl/g (0° C., 1 atm.).

This application is the US national phase of international applicationPT/JP2004/011403. filed 3 Aug. 2004, which designated the U.S. andclaims priority of JP 2003-20581 2, filed 4 Aug. 2003, the entirecontents of each of which ar hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to an alkali-free glass, particularly analkali-free glass utilized as a transparent glass substrate for a liquidcrystal display.

BACKGROUND ART

An alkali-free glass is employed as a transparent glass substrate for aliquid crystal display or the like. Such alkali-free glass is requiredto be free from bubbles constituting defects in the display.

The alkali-free gla is melted at a higher temperature in comparison withglass containing an alkali melted component, because of a higherviscosity of the molten glass. In melting the alkali-free glass, avitrifying reaction usually takes place at from 1200 to 1400° C., andbubble reduction and homogenization are executed at a high temperatureof 1500° C. or higher. Therefore, it is necessary to utilize a finingagent capable of releasing fining gas at least in a high temperatureregion where the bubble reduction and the homogenization are executed.Because of such situation, As₂O₃ capable of generating fining gas in awide temperature range has been widely employed as the fining agent forthe alkali-free glass. However, As₂O₃ is a hazardous material and it isdesired to reduce or totally replace such material.

Therefore, methods utilizing SO₃, Sb₂O₃, SnO₂, Cl₂ or the like as analternative fining agent for As₂O₃ are proposed (for example, patentreferences 1 and 2).

-   [Patent Reference 1]

JP-A-11-43350

-   [Patent Reference 2]

JP-A-2000-159541

DISCLOSURE OF THE INVENTION

The alternative fining agent mentioned above has enabled to bring anumber of bubble inclusion, called seed, of the glass to a practicallyacceptable level, but fewer bubble inclusion is required along with arecent increase in the size of the liquid crystal display screen.

An object of the present invention is to provide an alkali-free glasswhich is capable of reducing or totally eliminating As₂O₃ and which hasfewer bubble inclusion than that in the prior technology.

The present inventors have found that bubbles in the molten glass can becompletely eliminated or significantly reduced by including a specificamount of an inert gas component such as helium or neon, as a componentproviding a fining effect in the alkali-free glass, in the molten glassand have thus made the present invention.

More specifically, the present invention has the following composition.

(1) An alkali-free glass which comprises:

SiO₂ in an amount of from 40 to 70% by weight;

Al₂O₃ in an amount of from 6 to 25% by weight;

B₂O₃ in an amount of from 5 to 20% by weight;

MgO in an amount of from 0 to 10% by weight;

CaO in an amount of from 0 to 15% by weight;

BaO in an amount of from 0 to 30% by weight;

SrO in an amount of from 0 to 10% by weight;

ZnO in an amount of from 0 to 10% by weight,

each based on the total amount of said glass, and

helium and/or neon in an amount of from 0.0001 to 2 μl/g (0° C., 1atm.).

(2) The alkali-free glass according to the above (1), which furthercomprises a fining component.

(3) The alkali-free glass according to the above (2), wherein the finingcomponent is at least one selected from the group consisting of SO₃,Sb₂O₃, SnO₂ and Cl₂.

(4) The alkali-free glass according to the above (3), wherein SO₃ iscontained in an amount of from 0.0001 to 0.03% by weight based on thetotal amount of said glass.

(5) The alkali-free glass according to the above (3), wherein Sb₂O₃ iscontained in an amount of from 0.05 to 3% by weight based on the totalamount of said glass.

(6) The alkali-free glass according to the above (3), wherein SnO₂ iscontained in an amount of from 0.05 to 1% by weight based on the totalamount of said glass.

(7) The alkali-free glass according to the above (3), wherein Cl₂ iscontained in an amount of from 0.005 to 1% by weight based on the totalamount of said glass.

(8) A transparent glass substrate for a liquid crystal display which isobtainable by the alkali-free glass according to any one of the above(1) to (7).

In the invention, “alkali-free” means that alkali metal oxides (Li₂O,Na₂O, and K₂O) are present in an amount of 0.2% by weight or less.

BEST MODE FOR CARRYING OUT THE INVENTION

Unless otherwise indicated, the term “%” hereinafter means “% by weight”based on the total amount of glass. In addition, the term “% by weight”have a same meaning as “% by mass”.

The expression “X is contained in an amount of from 0 to Y %” means thatX is either not present, or is higher than 0% and up to Y %.

In the molten glass, the elements form a network state of a weak bondingforce, and show irregular relative positional changes involvingelongational, rotational and angular vibrations more vigorously at ahigher temperature. However, helium or neon, because of a closed-shellstructure of the electrons in the atomic structure, shows a very lowreactivity and a small dimension, as will be explained later.

Therefore, helium or neon, scarcely binding with the elementsconstituting the molten glass and having a sufficiently small dimensioncapable of passing through a gap in the vibrating network mentionedabove, can easily diffuse into a bubble present as a defect in themolten glass, without being affected by the surrounding elements.

Therefore, by contacting helium or neon with the molten glass includinga plurality of fine bubble defects, it is possible to rapidly expand thesize of the fine bubbles incorporated in the molten glass. As a result,the bubbles with an expanded size show a larger floating power and floatrapidly, whereby the molten glass is promptly fined. Helium or neon thusprovides a fining effect in the molten glass, and such effect isenhanced in a condition where the molten glass contains various finingagents to be explained later.

This is because, in addition to the fining effect of helium or neonitself and the fining effect of the various fining agents, a multiplyingeffect is obtained by diffusion of helium or neon in fine bubblesgenerated by the various fining agents.

Helium or neon to be employed in the invention, being classified asinert gas or rare gas and having a stable closed shell structure, ispresent in the state of a single-atom molecule. Helium is the lightestelement among the rare gases, shows a very small dimension in structureand a very weak Van der Waals attractive force, and remains in a liquidphase even at the absolute zero temperature without solidifying under anatmospheric pressure. Neon has a smaller dimension next to helium amongthe rare gases, and assumes a stable structure in a single-atom moleculeas in the case of helium.

Therefore, in a glass composition prepared by melting at a hightemperature following by cooling, helium or neon is present in a statetrapped in a pore of a glass network structure constituted by othercomponents.

Helium and/or neon is not involved in the formation of the glass networkstructure, but an amount of 0.0001 μl/g or higher singly or in a unitedamount in the glass provides a fining effect. Also an amount of 0.06μl/g or higher enables a secure fining effect. Also for realizing afining effect even under a severe condition wherein the glass has ahigher content of gasifyable components, there is more preferred acontent of 0.1 μl/g or higher which provides the molten glass with asufficient fining effect.

On the other hand, a content of 2 μl/g or less is desirable because itcan avoid re-boiling, when the glass composition is heated again. Anupper limit content not causing the re-boiling is preferably 1.5 μl/g orless, though it is variable depending on a glass composition and aheating condition. Such upper limit of 1.5 μl/g is shifted lower to 1.0μl/g in case of a glass composition also comprising a fining agent otherthan helium and/or neon, since the re-boiling is facilitated.

Therefore, following ranges are preferred for the content of helium andneon. When the glass composition does not comprise a fining agent otherthan helium and neon, a content range providing the fining effect evenunder a severe condition and not easily causing the re-boiling ispreferably 0.1 to 1.5 μl/g. On the other hand, when the glasscomposition comprises a fining agent in addition to helium and neon, therange is preferably 0.1 to 1.0 μl/g.

Helium or neon can be added to the glass composition of the inventionfor example by a method of utilizing a substance containing helium orneon at a high concentration or glass cullets containing helium or neonas a raw material, a method of melting the raw materials in a helium- orneon-containing atmosphere, or a method of contacting molten glass witha helium- or neon-containing atmosphere.

For contacting the molten glass with a helium- or neon-containingatmosphere, there can be employed a method of introducing helium or neoninto a container of molten glass, melting glass in a container with agas permeability and maintaining a helium- or neon-containing atmospherearound the container, or a method of bubbling helium or neon with arefractory nozzle.

In case of bubbling, a porous refractory material employed at an end ofthe nozzle facilitates efficient diffusion of helium or neon into theglass.

The alkali-free glass of the present invention preferably comprises afining agent component in addition to helium and/or neon in theaforementioned range.

The fining agent is not especially limited, but it is preferable atleast one selected from the group consisting of SO₃ (sulfate), Sb₂O₃,SnO₂ and Cl₂ (chloride).

The content of the fining agent as a remaining amount in the glass ispreferably 0.0001 to 0.03% for SO₃, 0.05 to 3% for Sb₂O₃, 0.05 to 1% forSnO₂ and 0.005 to 1% for Cl₂ individually.

The fining agents mentioned above may be employed singly, but arepreferably employed in a combination of two or more thereof in order toobtain a higher fining effect. A combination of the fining agentsincludes following examples:

(i) SO₃ in an amount of from 0.0001 to 0.03% and SnO₂ in an amount offrom 0.05 to 1%;

(ii) Sb₂O₃ in an amount of from 0.05 to 3% and SnO₂ in an amount of from0.05 to 1%;

(iii) Sb₂O₃ in an amount of from 0.05 to 3% and Cl₂ in an amount of from0.005 to 1%;

(iv) Sb₂O₃ in an amount of from 0.05 to 3%, SnO₂ in an amount of from0.05 to 1% and Cl₂ in an amount of from 0.005 to 1%;

(v) SO₃ in an amount of from 0.0001 to 0.03% and Cl₂ in an amount of0.005 to 1%; and

(6) SnO₂ in an amount of from 0.05 to 1% and Cl₂ in an amount of from0.005 to 1%.

Each fining agent mentioned above exhibits a high fining effect by beingpresent with helium and/or neon, and remains partly in the glasscomposition after cooling even if it is denatured by a pyrolysis or anoxidation-reduction reaction in high-temperature melting.

A sulfate decomposes at a temperature range of about 1200 to 1500° C.,and generates a large amount of fining gas (sulfur dioxide, oxygen gas)upon decomposition. SO₃ decomposes at a high temperature of 1400° C. andis optimum for a glass having a vitrifying process at a hightemperature, such as alkali-free glass. More specifically, SO₃ functionseffectively as a fining agent in case of melting glass having atemperature, corresponding to a viscosity of 10^(2.5) dPa·s, of 1500° C.or higher.

However, solubility of SO₃ in glass decreases with a decrease in thealkali content, and it is very low in case of an alkali-free glass.Stated differently, SO₃ releases a large amount of gas in the vitrifyingprocess, but the fining effect is reduced in a fining step after thevitrification since SO₃ remains in a smaller amount therein.

Sb₂O₃ and SnO₂ release a large amount of fining gas (oxygen gas) by achemical reaction involving a change in valence number of Sb ion and Snion. More specifically, Sb₂O₃ (trivalent) once changes to Sb₂O₅(pentavalent) at a low temperature range of several hundred degrees andreleases a large amount of fining gas upon returning to Sb₂O₃(trivalent) at about 1200 to 1300° C. Therefore the gas generated in thevitrifying process of the alkali-free glass can be expelled from themolten glass. Also SnO₂ (tetravalent) releases a large amount of fininggas upon changing to SnO (divalent) at 1400° C. or higher, and exhibitsits effect at a homogenizing melting at a higher temperature.

A chloride decomposes and evaporates in a temperature range of 1200° C.or higher to generate fining gas (chlorine gas etc.), and, showingvigorous decomposition and evaporation in a high temperature range of1400° C. or higher to generate a large amount of chlorine gas, is effectfor fining at a homogenizing melting.

Therefore, a combination of the fining agents having differenttemperature ranges for generating the fining gas enables to generating afining gas over a wide temperature range from the vitrifying reaction ata relatively low temperature to the homogenizing melting at a hightemperature, and achieves an even higher fining effect by the presenceof helium and/or neon at the same time.

The fining agent is not particularly restricted in a method of addition,and may be added to a glass batch or may be added later to the moltenglass. Otherwise it may be added at the same time as the addition ofhelium or neon. It is also possible to add the aforementioned componentinto the molten glass as an eluting component from a container at themelting or a refractory material immersed in the molten glass. It isfurthermore possible to obtain an optimum addition amount by adding thefining agent alternately with helium or neon or by gradually increasingor decreasing the amount of addition under confirmation of the finingeffect.

In the following there will be explained components other than thefining component in the alkali-free glass of the invention.

SiO₂ is a component constituting a network of the glass, and is presentin an amount of from 40 to 70%, preferably from 45 to 65%. When theamount of SiO₂ is 40% or more, it is preferable because it is easy tomaintain a good chemical resistance and it is difficult to cause a lowstrain point to maintain a good heat resistance. While, the amountthereof is 70% or less, it is preferable because a viscosity at a hightemperature is difficult to be increased thereby it is easy to maintaina good melting property, and it can prevent a devitrifying substancesuch as cristobalite from being precipitated.

Al₂O₃ is a component improving a heat resistance and a devitrificationresistance of the glass, and is present in an amount of from 6 to 25%,preferably from 10 to 20%. When the amount of Al₂O₃ is 6% or more, adevitrifying temperature is difficult to be significantly increased andit can prevent a devitrifying substance from being generated in theglass. While, the amount thereof is 25% or less, it is preferablebecause it is easy to maintain a good acid resistance, especially a goodresistance to buffered hydrofluoric acid, thereby it can prevent a whiteturbidity from being generated on the glass surface.

B₂O₃ is a component functioning as a flux and reducing viscosity therebyfacilitating melting, and is present in an amount of from 5 to 20%,preferably from 6 to 15%. When the amount of B₂O₃ is 5% or more, it ispreferable because a sufficient effect as the flux can be obtained.Moreover, the amount thereof is 20% or less, it is preferable because itis easy to maintain a good resistance to hydrochloric acid and it isdifficult to cause a low strain point thus to maintain a sufficient heatresistance.

MgO is a component reducing the viscosity at high temperature withoutlowering the strain point thereby facilitating the glass melting, and ispresent in an amount of from 0 to 10%, preferably from 0 to 7%. When theamount of MgO is 10% or less, it is preferable because it is easy tomaintain a goon resistance of glass to buffered hydrofluoric acid.

CaO functions similarly as MgO, and is present in an amount of from 0 to15%, preferably from 0 to 10%. When the amount of CaO is 15% or less, itis preferable because it is easy to maintain a good resistance of glassto buffered hydrofluoric acid.

BaO is a component elevating the chemical resistance and improving thedevitrifying property, and is present in an amount of from 0 to 30%,preferably from 0 to 20%. When the amount of BaO is 30% or less, it ispreferable because it is difficult to cause a low strain point thusmaintaining a good heat resistance.

SrO has an effect similar to that of BaO, and is present in an amount offrom 0 to 10%, preferably from 0 to 7%. When the amount of SrO is 10% orless, it is preferable because it is easy to improve a devitrifyingproperty.

ZnO is a component improving a resistance to buffered hydrofluoric acidand a devitrifying property, and is present in an amount of from 0 to10%, preferably from 0 to 7%. When the amount of ZnO is 10% or less, itis preferable because it is difficult to cause devitrification of theglass, and it is difficult to cause a low strain point thus maintaininga good heat resistance.

A total amount of MgO, CaO, BaO, SrO and ZnO is preferably from 5 to30%. When the amount is 5% or more, it is preferable because a viscosityat a high temperature is difficult to be increased, thereby maintaininga melting property, and it becomes difficult to cause devitrification ofthe glass. On the other hand, when the amount thereof is 30% or less, itis preferable because desirable heat resistance and acid resistance canbe obtained.

In addition to the foregoing components, ZrO₂, TiO₂, Fe₂O₃ etc. may beadded up to 5% in a total amount.

In the following, a method for producing the alkali-free glass of thepresent invention will be described.

At first, there is a prepared glass batch so as to obtain a glass of theaforementioned composition. In case of introducing helium or neon, rawmaterials prepared correspondingly in advance are used. Also in case ofusing a fining agent such as SO₃, Sb₂O₃, SnO₂, or Cl₂, there may beadded a sulfate, Sb₂O₃, SnO₂, or a chloride to the glass batch. As asulfate, BaSO₄, CaSO₄ etc. may be utilized. Also as a chloride, BaCl₂,SrCl₂, CaCl₂ etc. may be utilized.

An amount of the sulfate is preferably from 0.005 to 1% by weight incalculation as SO₃ based on 100% by weight of the glass batch, and suchamount of addition provides SO₃ of from 0.0001 to 0.03% in the glass.

When the amount of sulfate is 0.005% or more, it is preferable becausethe gas generated in the vitrifying process is easy to expel. While,when the amount thereof is 1% or less, it is preferable because it isdifficult to cause re-boiling, whereby bubbles do not remain in theglass.

A preferred amount of the sulfate is preferably from 0.01 to 1% incalculation as SO₃, more preferably from 0.05 to 1% and furtherpreferably from 0.05 to 0.5%. A preferred amount of SO₃ is from 0.0001to 0.03%, more preferably from 0.0005 to 0.03%, and further preferablyfrom 0.0005 to 0.01%.

An amount of Sb₂O₃ is preferably from 0.01 to 3% by weight based on 100%by weight of the glass batch. When the amount of Sb₂O₃ is 0.01% or more,it is preferable because the gas generated in the vitrifying process iseasy to expel. While, the amount thereof is 3% or less, it is preferablebecause it is difficult to cause devitrification of the glass. A morepreferred amount of Sb₂O₃ is from 0.05 to 2%.

An amount of SnO₂ is preferably 0.05 to 1% by weight based on 100% byweight of the glass batch. When the amount of SnO₂ is 0.05% or more, itis preferable because the bubbles remaining in the molten glass becomeeasy to remove during the fining process. While, the amount thereof is1% or less, it is preferable because it is difficult to causedevitrification of the glass. A preferred amount of SnO₂ is 0.1 to 0.5%.

An amount of chloride is preferably from 0.01 to 2% by weight incalculation as Cl₂, based on 100% by weight of the glass batch, and suchamount of addition provides Cl₂ in an amount of from 0.005 to 1% in theglass. When the amount of chloride is 0.01% or more, it is preferablebecause the bubbles remaining in the molten glass become easy to expelat the homogenizing melting. While, the amount thereof is 2% or less, itis preferable because an excessively large amount of evaporation is notgenerated, thereby it is difficult to denaturalize the glass. Apreferred amount of chloride is 0.05 to 1% in calculation as Cl₂, morepreferably 0.05 to 0.5%, and a preferred content of Cl₂ is 0.01 to 0.5%,more preferably 0.01 to 0.3%.

In the invention, it is also possible to utilize a fining agent otherthan those in the foregoing, such as a fluoride. Fe₂O₃ is a componentalso having a fining effect, but is maintained at 800 ppm or less,preferably 500 ppm or less, since a large amount of Fe₂O₃ reduces thevisible light transmittance of the glass, unfavorably for application ina display.

Then the prepared glass batch is molten. In case of introducing heliumor neon at the melting of the glass, a suitable method can be selectedfrom the aforementioned various methods.

Thereafter, the molten glass is formed into a desired shape. Forapplication in a display, a thin sheet is formed for example by a fusionmethod, a down-draw method, a floating method or a roll-out method.

An alkali-free glass of the invention can be obtained in this manner. Inaddition, the glass of the invention comprises:

SiO₂ in an amount of from 40 to 70% by weight;

Al₂O₃ in an amount of from 6 to 25% by weight;

B₂O₃ in an amount of from 5 to 20% by weight;

MgO in an amount of from 0 to 10% by weight;

CaO in an amount of from 0 to 15% by weight;

BaO in an amount of from 0 to 30% by weight;

SrO in an amount of from 0 to 10% by weight;

ZnO in an amount of from 0 to 10% by weight,

each based on the total amount of said glass, and

helium and/or neon in an amount of from 0.0001 to 2 μl/g (0° C., 1atm.).

A content of helium or neon in the glass is obtained by charging(dropping) a sample of 10 to 500 mg in a Mo crucible placed in a furnaceheated to 1600° C., holding the sample for 20 minutes and measuring gas,released under a vacuum of 10⁻⁹ Torr, with a high-sensitivity rare gasmass analyzer.

EXAMPLES

In the following the alkali-free glass of the present invention will beexplained in detail by examples and comparative examples, but theinvention should not be construed as being limited to these Examples.

Example 1

Tables 1 and 2 respectively show Examples (samples Nos. 1 to 6) of theinvention and Comparative Examples (samples Nos. 7 to 12).

TABLE 1 Sample 1 2 3 4 5 6 (% by weight) SiO₂ 60.0 54.0 56.3 58.7 62.364.4 Al₂O₃ 16.0 19.6 10.7 16.5 17.5 19.5 B₂O₃ 8.5 10.5 8.4 8.3 8.5 5.5MgO 4.0 — — 3.7 4.5 0.3 CaO 1.0 3.1 5.4 1.0 — 5.9 SrO 3.5 8.9 4.2 3.10.6 0.6 BaO 6.0 1.8 13.0 5.8 1.1 0.3 ZnO 1.0 — 1.3 0.9 2.7 — (μl/g) He1.980 0.982 0.498 0.004 0.132 NA Ne NA NA NA NA 0.183 0.465 bubbles <1.05.2 6.5 7.5 3.5 1.3 (number/100 g)

TABLE 2 Sample 7 8 9 10 11 12 (% by weight) SiO₂ 60.0 54.0 56.3 58.762.3 64.4 Al₂O₃ 16.0 19.6 10.7 16.5 17.5 19.5 B₂O₃ 8.5 10.5 8.4 8.3 8.55.5 MgO 4.0 — — 3.7 4.5 0.3 CaO 1.0 3.1 5.4 1.0 — 5.9 SrO 3.5 8.9 4.23.1 0.6 0.6 BaO 6.0 1.8 13.0 5.8 1.1 0.3 ZnO 1.0 — 1.3 0.9 2.7 — (μl/g)He <0.00001 <0.00001 <0.00001 <0.00001 <0.00001 <0.00001 Ne <0.00001<0.00001 <0.00001 <0.00001 <0.00001 <0.00001 bubbles 132 155 168 212 120295 (number/100 g)

Each sample was prepared in the following manner. At first, a batchprepared in advance for a predetermined composition corresponding to 500g of glass was charged in a platinum crucible, which was placed in anatmospheric furnace with an air-tight structure for 4 hours at 1600° C.Then, an atmospheric gas with a He or Ne content of 95% or higher wasintroduced into the furnace, and the temperature was further maintainedfor 30 minutes.

Thereafter, glass was taken out, molded in a glass-like carbon mold andcooled. Samples Nos. 7 to 12 constituting Comparative Examples wereprepared in the same conditions as above except for employing air as themelting atmosphere.

Then a number of bubbles remaining in the sample was measured with astereo microscope of a magnification of 20 to 100 times, while thesample was held in an immersion liquid of a refractive index same asthat of the glass.

A content of helium or neon in the glass was obtained by charging(dropping) a sample in a Mo crucible placed in a furnace heated to 1600°C., holding the sample for 20 minutes and measuring gas, released undera vacuum of 10⁻⁹ Torr, with a double-collector rare gas mass analyzer(VG5400).

In these tables, NA means “not analyzed”.

Example 2

Tables 3 to 8 show Examples of the invention (samples Nos. 13 to 43).

TABLE 3 Sample 13 14 15 16 17 18 (% by weight) SiO₂ 60.0 54.0 56.3 58.762.3 64.4 Al₂O₃ 16.0 19.6 10.7 16.5 17.5 19.5 B₂O₃ 8.5 10.5 8.4 8.3 8.55.5 MgO 4.0 — — 3.7 4.5 0.3 CaO 1.0 3.1 5.4 1.0 — 5.9 SrO 3.5 8.9 4.23.1 0.6 0.6 BaO 6.0 1.8 13.0 5.8 1.1 0.3 ZnO 1.0 — 1.3 0.9 2.7 — SO₃0.0004 0.0006 0.0014 0.0048 0.0096 0.0125 SnO₂ 1.0 0.6 0.3 0.15 0.1 0.05(μl/g) He 1.809 0.802 0.434 0.006 0.114 NA Ne NA NA NA NA 0.193 0.482bubbles <1.0 <1.0 1.4 1.5 2.5 4.5 (number/100 g)

TABLE 4 Sample 19 20 21 22 23 (% by weight) SiO₂ 58.4 56.2 54.6 59.362.4 Al₂O₃ 16.5 11.0 19.9 16.4 17.8 B₂O₃ 9.0 8.3 10.6 8.5 8.4 MgO — — —3.9 4.7 CaO 2.1 5.4 3.0 0.8 — SrO 6.5 4.0 9.0 3.0 0.8 BaO 3.5 13.2 2.05.9 1.3 ZnO 0.5 1.5 — 1.0 3.1 Sb₂O₃ 0.2 0.4 1.3 1.7 2.5 SnO₂ 0.6 0.2 0.40.7 1.0 (μl/g) He 0.431 0.644 0.524 0.724 0.982 Ne 0.001 NA NA 0.020 NAbubbles 2.2 3.0 1.0 <1.0 <1.0 (number/100 g)

TABLE 5 Sample 24 25 26 27 28 (% by weight) SiO₂ 65.3 57.7 48.0 56.059.0 Al₂O₃ 19.8 15.7 11.0 10.5 15.0 B₂O₃ 5.6 8.5 14.5 5.5 10.5 MgO 0.33.9 — 2.0 0.5 CaO 6.2 0.8 — 3.5 4.5 SrO 0.5 3.3 — 6.0 3.0 BaO 0.4 6.125.0 15.0 6.0 ZnO — 1.1 — — — Sb₂O₃ 0.1 0.6 1.0 1.5 2.4 Cl₂ 0.06 0.3 0.20.4 0.5 (μl/g) He 0.221 0.662 0.754 0.945 1.325 Ne NA NA NA 0.061 0.170bubbles 3.8 1.9 1.5 <1.0 <1.0 (number/100 g)

TABLE 6 Sample 29 30 31 32 33 (% by weight) SiO₂ 58.0 63.0 66.0 54.064.5 Al₂O₃ 16.0 18.0 19.5 19.5 19.0 B₂O₃ 8.5 8.0 5.5 10.5 6.0 MgO 1.05.0 — — 0.5 CaO 4.0 — 6.5 3.0 6.0 SrO 2.0 1.0 0.5 8.5 0.5 BaO 9.5 1.00.5 2.0 0.5 ZnO — 3.0 0.5 — — Sb₂O₃ 0.5 0.3 0.9 0.1 1.9 SnO₂ 0.5 0.9 0.30.6 0.1 Cl₂ 0.5 0.3 0.1 0.1 0.1 (μl/g) He 0.186 0.665 0.552 0.724 0.358Ne NA 0.002 0.001 NA NA bubbles 1.2 <1.0 <1.0 <1.0 <1.0 (number/100 g)

TABLE 7 Sample 34 35 36 37 38 (% by weight) SiO₂ 58.4 56.2 54.6 59.362.4 Al₂O₃ 16.5 11.0 19.9 16.4 17.8 B₂O₃ 9.0 8.3 10.6 8.5 8.4 MgO — — —3.9 4.7 CaO 2.1 5.4 3.0 0.8 — SrO 6.5 4.0 9.0 3.0 0.8 BaO 3.5 13.2 2.05.9 1.3 ZnO 0.5 1.5 — 1.0 3.1 SO₃ 0.0102 0.0068 0.0047 0.0015 0.0003 Cl₂0.01 0.08 0.14 0.24 0.32 (μl/g) He 0.412 0.512 0.489 0.701 0.893 Ne0.001 NA NA 0.018 NA bubbles 2.2 1.3 1.1 <1.0 <1.0 (number/100 g)

TABLE 8 Sample 39 40 41 42 43 (% by weight) SiO₂ 65.3 57.7 48.0 56.059.0 Al₂O₃ 19.8 15.7 11.0 10.5 15.0 B₂O₃ 5.6 8.5 14.5 5.5 10.5 MgO 0.33.9 — 2.0 0.5 CaO 6.2 0.8 — 3.5 4.5 SrO 0.5 3.3 — 6.0 3.0 BaO 0.4 6.125.0 15.0 6.0 ZnO — 1.1 — — — Cl₂ 0.03 0.18 0.09 0.30 0.41 SnO₂ 0.05 0.10.3 0.4 0.9 (μl/g) He 0.234 0.602 0.790 0.984 1.143 Ne NA NA NA 0.0480.151 bubbles 3.8 1.9 <1.0 <1.0 <1.0 (number/100 g)

The samples were prepared and evaluated in the same manner as in Example1.

As a result, the samples of the examples containing helium or neonshowed 4.6 bubbles or less per 100 g and a sufficient fining effectcould be confirmed.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

This application is based on a Japanese patent application filed on Aug.4, 2003 (Application No. 2003-205812), the contents thereof being hereinincorporated by reference.

INDUSTRIAL APPLICABILITY

As explained in the foregoing, the alkali-free glass of the presentinvention, being free from bubbles constituting defects in display, issuitable for a transparent glass substrate for a display, particularlyfor a transparent glass substrate for a liquid crystal display.

In addition to the application for the liquid crystal display, it isapplicable as a glass substrate for other flat panel displays such as anelectroluminescent display, a cover glass for image sensors such as acharge-coupled device, an equal-size proximity solid-state image pickupdevice or a CMOS image sensor, or a glass substrate for a hard disk or afilter.

1. An alkali-free glass which comprises: SiO₂ in an amount of from 40 to70% by weight; Al₂O₃ in an amount of from 6 to 25% by weight; B₂O₃ in anamount of from 5 to 20% by weight; MgO in an amount of from 0 to 10% byweight; CaO in an amount of from 0 to 15% by weight; BaO in an amount offrom 0 to 30% by weight; SrO in an amount of from 0 to 10% by weight;ZnO in an amount of from 0 to 10% by weight, each based on the totalamount of said glass, and helium and/or neon in an amount of from 0.0001to 2 μl/g (0° C., 1 atm.).
 2. The alkali-free glass according to claim1, which further comprises a fining component.
 3. The alkali-free glassaccording to claim 2, wherein the fining component is at least oneselected from the group consisting of SO₃, Sb₂O₃, SnO₂ and Cl₂.
 4. Thealkali-free glass according to claim 3, wherein SO₃ is contained in anamount of from 0.0001 to 0.03% by weight based on the total amount ofsaid glass.
 5. The alkali-free glass according to claim 3, wherein Sb₂O₃is contained in an amount of from 0.05 to 3% by weight based on thetotal amount of said glass.
 6. The alkali-free glass according to claim3, wherein SnO₂ is contained in an amount of from 0.05 to 1% by weightbased on the total amount of said glass.
 7. The alkali-free glassaccording to claim 3, wherein Cl₂ is contained in an amount of from0.005 to 1% by weight based on the total amount of said glass.
 8. Atransparent glass substrate for a liquid crystal display which isobtainable by the alkali-free glass according to claim 1.